The present invention relates to a system, termed a pantograph, for supplying an electric-traction train with electric current by way of overhead conductors or overhead contact lines.
More precisely, the invention relates to systems enabling the electrical contact between the upper element of the pantograph, termed horned slipper holder, and the overhead contact line to be improved.
Indeed, it is important for the said electrical contact to be established permanently during periods of use and, moreover, it is desirable for this contact to provide as constant a resistance as possible to the passage of the electric current whatever the circumstances and, in particular, whatever the speed of the train.
With a view to obtaining a uniform electrical contact between the horned slipper holder and the overhead contact line, it is known to use systems whose function is to apply the horned slipper holder against the overhead contact, line with a certain elasticity caused, for example, by the presence of springs, the latter enabling certain environmental variations to be withstood without the contact being affected unduly by them.
In particular, it is known to use a device of the type called the air-cushion type, comprising a pneumatic member consisting of two parallel cover plates connected at their periphery by an element in the form of an elastic bellows, the first cover plate being integral with the structure of the driving car and the second cover plate being able to undergo a displacement of limited magnitude.
When the bellows is distended with a gas, such as compressed air at a given pressure, the folds of the bellows are expanded, which causes the movable cover plate to be displaced. This displacement is accompanied by a rotational movement of the axis of a lower arm of the pantograph, this rotational movement enabling a certain pressure to be exerted by the horned slipper holder against the overhead contact line.
When functioning, with the locomotive running on the track, the said device plays, to a certain extent, the role of a return spring with particular properties.
In order to ensure an approximately horizontal movement of the movable cover plate, it is generally made integral with the end of a substantially vertical rod, fastened at its lower end, in an articulated manner, to the structure of the driving car. The above rod is relatively long and capable, at its upper end, of a substantially horizontal range of movement, which enables it to serve as a guide for the movable cover plate when the latter is displaced by a limited amplitude. A rod must be used which is sufficiently long that the displacement of the cover plate is comparable to a segment of a straight line.
Experience shows that the device of the above air-cushion type and more particularly its guide system, has various disadvantages:
the guide system is relatively complex and heavy, which increases the inertia of the assembly and affects the performance of the pantograph to the extent that an increase in the inertia results in the whole system having a longer response time to disturbances,
the length of the rod, which is entailed by the need to have a displacement at its end which is comparable to a segment of a straight line, makes the guide system bulky,
the guide system does not prevent a certain buckling of the bellows from occurring, which may introduce a deviation in the displacement of the cover plate when the device returns to a position of equilibrium from which it has temporarily been moved away, and consequently an unjustified deviation in the application pressure of the horned slipper holder;
the guide system is exposed to dusts, aggressive agents and atmospheric precipitations, and requires relatively frequent monitoring and maintenance operations.
The object of the present invention is to propose a novel device for a pantograph enabling the above disadvantages to be reduced very considerably.